The hit movie Signs has managed to spin crop circles, those giant geometric formations of bent plants, into the supernatural phenomenon du jour. For most folks, the discussion is about whether crop circles are man-made -- or messages from outer space. Enthusiasts like Nancy Talbott, however, look for a scientific explanation.

Based in Cambridge, Mass, the former Baltimorean is president of BLT Research Team Inc., a nonprofit organization conducting scientific inquiries into crop circles. So far, the group has documented consistent physical changes in plants and soils in its quest to determine what energy -- or energy systems -- are responsible for making them.

A music producer with experience in psychology research, Talbott became mystified by crop circles in the late 1980s. Then she discovered the plant studies of Michigan biophysicist W. C. Levengood, the scientist who documented abnormalities in crop circle plants that made them distinct from others in the same field. Talbott volunteered to help out. Before long, circle site sampling had expanded to reveal perplexing abnormalities in the soil.

With the help of John Burke, a New York businessman with strong interest in geomagnetic and electromagnetic theory, Talbott created an international network of field workers to obtain samples from circles to send to Levengood's Michigan lab.

Data from nearly 300 circles in seven countries was analyzed. More than 90 percent of the crop formations sampled show recurring abnormalities in crop circle plants and also magnetic material in the soil. Talbott writes that these changes are "consistent with exposure to an intense and complex energy system which emits heat [possibly microwaves] along with highly unusual electrical pulses and strong magnetic fields."

We asked Talbott, 63, to talk a little about crop circles' enduring mystery:

In the movie Signs, crop circles indicate aliens visiting Earth. What do you think they signify?

I don't know. Crop circles indicate something we don't currently understand taking place. If I thought I knew what it was, the scientific work wouldn't be necessary. The media has very successfully created the notion that the answer to the crop circle mystery has to be hoaxes -- "pranks with planks" we call them -- or ETs. Our work shows we can rule out planks and boards, but not little green men. ... We suggest there is an enormous range within those two extremes that needs to be examined.

Why are so many crop circles reported in southern England?

The largest deposit of chalk in the world is under southern England. Chalk is the most porous rock. As surface water percolates down through that chalk to the aquifer below, it sets up an electrical charge. ... As summer progresses [and the water table lowers], the ground's electrical charge [usually] increases. Most circles tend to occur later in the summer.

Are there similar conditions in North America?

In North America, crop circles frequently occur over limestone deposits. After chalk, limestone is the most porous rock. ... You find the most circles in the U.S. from July through October.

How many circles have been reported?

Some people would say there have been 10,000 to 15,000 of these things actually reported around the world. As more people study this, we hear of more. But it's very clear these events are not new. In 1880 the science journal Nature published a report of crop circles in southern England. Robert Plot, another British scientist, wrote a book in 1660 describing not just simple circles but circles with squares, circles with rings, spirals. ... He ended up thinking the circles were caused by some strange form of lightning.

What about the designs?

Most genuine crop circles are not circles at all. They are ellipses. They are so big that they appear to be circles. In England, where you have the most elaborate formations, you also have the greatest number of man-made events. ... We stopped sampling aggressively in England because there are many self-confessed hoaxers there, and the expenses involved in examining hoaxes is the same as for the real thing. We have turned to countries like Canada where there is less evidence of man-made events.

How do you tell real from fake?

The results from the past 10 years of research consistently show elongated plant stem nodes and the presence of expulsion cavities [holes blown out at the nodes] in crop circle plants. Additionally, tiny magnetic spheres are regularly found in crop circle soils -- primarily around the edges of the circles. Using planks and boards to create circles can cause fractures and breaks in the plants. With the real McCoy, the plants aren't broken. They are bent over, usually at the base.

Mysterious circles also appear in the ice on ponds or lakes. Do other surfaces also record such formations?

There are only a moderate number of ice circles reported each year. Crop circles have been reported in every type of vegetation, even in groves of trees. They've been seen in all vegetables: soybeans, full-grown corn, potatoes, onions, carrots, string beans. There have been cases reported in the snow or the sand that we suspect are the same phenomenon.

What does your research show about the energy that makes these formations?

Microwaves -- or some other heating agent -- are striking at the plants, heating up the internal moisture in the plant stems the same way your home microwave heats up the moisture inside your food. Levengood's hypothesis is that the microwaves are coming from a highly charged plasma system -- essentially electrified air. The northern lights is one example of a plasma system, sunspots are another.

Until recently, scientists thought lightning was the only instance of plasma discharged onto the earth's surface. There may be more interaction between upper and lower atmospheres than previously thought. The crop circle phenomenon may come from that.

Our [latest] research shows an increase in crystallinity in the clay minerals at these sites. This sort of change normally is found in sedimentary rock, which has tons of pressure from overlying rock heated over thousands of years. As far as we know, it has never been seen in surface soil before. ... It appears we are looking at an energy which can affect plants one way and soil another -- or at a very intense energy that would exist for only a nanosecond. Either way, we've got a conundrum.

Do you feel like an explorer?

It's a marvelous adventure to be discovering the physical attributes of whatever this energy system is. I think of this work as the story of the blind men describing the elephant. We're like the man who has the trunk. As we go along with crop circles, we learn more and more about that trunk. A biologist studying soil microbes might come up with the tail of this creature. Some other scientist might have an ear. Eventually, more and more of the elephant emerges -- a heretofore unknown energy system. There's a lot more to be done here.

For more information, see the organization's Web site, www.bltresearch.com.